Portable roll-up signs are currently used by the Texas Department of Transportation (TxDOT) for identification of short-term maintenance/work zones and emergency operations. These signs have fiberglass frames to directly support diamond-shaped and rectangular flexible sign faces. It has been frequently reported that the fiberglass frames have failed due to bending caused by natural wind or gust generated by passing vehicles.
The cost of these failures is more than the marginal cost of replacing the broken frame members. It includes the safety cost to workers and the traveling public. Research studies to date on sign structures have focused on permanent signs with rigid faces. However, there has been little formal and in-depth research on wind loading on roll-up signs with flexible facing materials.
This research project was proposed to address three major issues: (1) understanding the nature of wind loading on portable roll-up signs, (2) identifying alternative materials for fiberglass frames, and (3) developing modified/new designs of portable roll-up signs.
The work performed under this project revealed that the vertical frames failed due to progressive cracking at the fiber-matrix interfaces caused by torsion, instead of bending. Therefore, it was determined to increase the torsional stiffness of vertical frames by wrapping high-strength carbon fiber sheets around the existing fiberglass frames in a pre-determined direction to improve the resistance to wind loading.
Prototype roll-up signs with the modified frame design were manufactured in the laboratory and were subjected to various tests including the full-scale vehicle impact tests per MASH impact performance criteria. The test results showed that the modified design showed better serviceability as well as higher resistance to torsion as compared to the original design. In addition, the prototype roll-up signs met MASH impact performance criteria.
The outcome of the project can lead to a significant reduction of the cost for replacing failed roll-up signs, and more importantly, help improve the safety of workers and traveling public in maintenance/work zones.